I think so that hypothesis is for isotopes and atomic mass.
If you have a neutral atom (like you normally would) then the number of electrons is equal to the number of protons. If you had more electrons then the charge would be negative. In this case, you would have 20 electrons.
The correct awnser would be D , hope this helps!
Answer:
Following are the responses to the given choices:
Explanation:
For point a:
Using the acid and base which are strong so,
moles of 
(from
)
moles of 
(from 
)
So, 
i.e. 
mol of 
in excess in total volume 
i.e. concentration of 
![p[OH^{-}] = -\log [OH^{-}] = -\log [2 \times 10^{-4}\ mol] = 3.70](https://tex.z-dn.net/?f=p%5BOH%5E%7B-%7D%5D%20%3D%20-%5Clog%20%5BOH%5E%7B-%7D%5D%20%3D%20-%5Clog%20%5B2%20%5Ctimes%2010%5E%7B-4%7D%5C%20mol%5D%20%3D%203.70)
Since, 
so,
For point b:
moles of = from point a 
moles of (from):
1 mol neutralizes 1 mol of
So, 
i.e. 
in excess in the total volume of 
i.e. concentration of
Hence, ![pH = -\log [H^+] = -\log[2 \times 10^{-4}] = 3.70](https://tex.z-dn.net/?f=pH%20%3D%20-%5Clog%20%5BH%5E%2B%5D%20%3D%20-%5Clog%5B2%20%5Ctimes%2010%5E%7B-4%7D%5D%20%3D%203.70)
